1. Field of Invention
The present invention is generally related to modems, and more particularly to digital modems.
2. Description of the Related Art
Digital subscriber line (DSL) technologies are being called on to provide large bandwidth, e.g. up to 100 Mbps links to homes and offices, for video on demand, teleconferencing, and other high throughput applications. To meet these elevated data rates DSL communications protocols such as discrete multitone (DMT) have been developed. In DMT communications each channel is split into sub-channels each with its own tone or sub-carrier to which a corresponding number of bits of the communication stream is assigned. The errorless transport of these bits on communication channels with low signal to noise ratios necessitated by the high data rates, requires extensive error correction overhead, which add redundant bits to the transmitted data to aid in the recovery of the errored data at the receiver. Forward error correction is typically combined with interleaving which provides additional levels of protection to what is known as ‘impulse noise’ on the communication channel. Interleaving spreads adjacent bits in the transmit stream over intervals greater than the duration of expected impulse noise thereby improving the error-correction performance.
Both interleave and forward error correction parameters vary depending on the communication standard, operator constraints and line constraints. Adjustments to one parameter typically effect others, and may significantly alter the performance of the communication channel.
What is needed are means for quickly and precisely determining the optimal parameters for encoding and interleaving the data on a communication channel.